Optical system for stereoscopic rigid endoscope

Abstract

An optical system for stereoscopic rigid endoscope is provided with first and second objective optical systems arranged to have a predetermined clearance therebetween and an optical path combining system that polarizes light passed through the first and second objective optical systems in directions perpendicular to each other. The optical path combining system parallelly shifts the optical axes of the first and second objective optical systems so that they coincide with each other. The shifting directions of the optical axes form an angle less than 90 degrees. A relaying optical system is provided inside the insertion unit of the endoscope. An optical axis of the relaying optical system is coaxial with the combined optical axes. An optical image separating system separates the light passed through the relaying optical system into first and second components that passed through the first and second objective optical systems and polarized by the optical path combining system, respectively.

1. An optical system for a stereoscopic rigid endoscope configured to form a pair of images of an object located at a position facing an insertion unit of the endoscope on a proximal side of the insertion unit, the endoscope comprising:
 a first objective optical system and a second objective optical system which are provided inside the insertion unit and are located at positions having the same distance from a tip of the insertion unit, the first objective optical system and the second objective optical system having a predetermined clearance therebetween; 
 an optical path combining system that polarizes light passed through the first objective optical system and light passed through the second objective optical system in directions perpendicular to each other, the optical path combining system parallelly shifting the optical axes of the first objective optical system and the second objective optical system by a predetermined amount so as to coincide with each other, an angle formed between a shifting direction of the first objective optical system and a shifting direction of the second objective optical system being equal to or less than 90 degrees; 
 a relaying optical system provided inside the insertion unit and having an optical axis that is coaxial with the optical axes of the first objective optical system and the second objective optical system made coaxial by the optical path combining system, the relaying optical system relaying the image formed by each of the first objective optical system and the second objective optical system from the position in the vicinity of the distal end of the insertion unit to a position in the vicinity of the proximal end of the insertion unit; and 
 an optical image separating system that obtains the image formed with the light passed through the first objective optical system and the image formed with light passed through the second objective optical system separately by separating the light passed through the relaying optical system into a first component that has passed through the first objective optical system and polarized by the optical path combining system and a second component that has passed through the second objective optical system and polarized by the optical path combining system from each other. 
 
   
   
     2. The optical system according to  claim 1 ,
 wherein the optical path combining system includes: 
 a first reflection surface and a second reflection surface that bend the optical axis of the first objective optical system in a cranked manner to parallelly shift the optical axis of the first objective optical system; 
 a third reflection surface that bends the optical axis of the second objective optical system perpendicularly; and 
 an optical path combining surface that serves to shift the optical axis of the second objective optical system by the predetermined amount so that the optical axis of the second objective optical system coincides with the optical axis of the first objective optical system by: 
 polarizing the light passed through the first objective optical system and reflected by the first reflection surface and the second reflection surface and is directed to the relaying optical system to in a first polarization direction; and 
 perpendicularly reflecting a component polarized in a second polarization direction which is perpendicular to the first polarization direction from among light passed through the second objective optical system and reflected by the third reflection surface so as to be directed to the relaying optical system. 
 
   
   
     3. The optical system according to  claim 1 , wherein a condition:
   0.75<φ 0 /φ r <1.1, 
 
     where, φ 0  denotes a maximum effective diameter of the first and second objective optical systems and φ r  denotes a maximum effective diameter of the relaying optical system. 
   
   
     4. The optical system according to  claim 3 , wherein the angle formed between the shifting directions of the optical axes of the first and second objective optical systems satisfies a condition below:
   0.586<sin(θ/2)<0.675, 
 
     where θ denotes the angle. 
   
   
     5. The optical system according to  claim 1 , wherein the optical axes of the first and second objective optical systems before shifted by the optical path combining system are substantially parallel with the optical axis of the relaying optical system. 
   
   
     6. The optical system according to  claim 1 , wherein the optical axis of the relaying optical system is shifted with respect to the central axis of a sheath in which the first and second objective optical system, the optical path combining system and the relaying optical system are accommodated. 
   
   
     7. The optical system according to  claim 1 , wherein the optical image separating system includes a polarization beam splitter. 
   
   
     8. The optical system according to  claim 7 , further comprising a pair of imaging devices that capture the images formed with the light passed through the first objective optical system and the light passed through the second objective optical system, respectively, one of the pair of imaging devices being provided on an optical path of the light reflected by the polarization beam splitter, the other of the pair of imaging devices being provided on an optical path of the light passed through the polarization beam splitter. 
   
   
     9. The optical system according to  claim 1 ,
 wherein the optical image separating system includes a liquid crystal shutter that selectively allows the light passed through the first objective optical system and polarized by the optical path combining system and the light passed through the second objective optical system and polarized by the optical path combining system alternately at every predetermined interval; and 
 wherein the endoscope further includes an imaging device that is located on an image side with respect to the liquid crystal shutter and captures the image formed with light passed through the first objective optical system and the image formed with the light passed through the second objective optical system alternately at every predetermined interval.